This invention concerns a high-yield process for making alpha-olefin polymers or copolymers with high isotacticity index, by polymerization of an alpha-olefin containing 3 to 8 carbon atoms, sequence copolymerization of such alpha-olefins with one another and/or with ethylene, or copolymerization of mixtures of such alpha-olefins with one another and/or with ethylene, the mixture containing at least 85 and preferably at least 90 mole percent of one of these alpha-olefins, using a modified Ziegler-Natta catalyst consisting of a titanium chloride combined with an organic aluminium compound, and in the presence of a stereospecificity additive.
Polymerization of an alpha-olefin containing 3 or more atoms, such as propylene, using a Ziegler-Natta catalyst consisting of a titanium chloride, such as titanium trichloride, combined with an organic aluminium compound, such as alkyl aluminium and alkyl aluminium chloride, is known to produce a polymerisate containing a polymer fraction with a crystalline structure under X-ray examination, alongside a polymer fraction with an amorphous structure under such examination. The polymer fraction with a crystalline structure, which consists of sterically ordered macromolecular chains, is known as isotactic polymer, while the polymer fraction with an amorphous structure, which consists of sterically disordered macromolecular chains, is known as atactic polymer.
For industrial purposes, isotactic polymers or copolymers of alpha-olefins containing 3 or more carbon atoms are most useful, and attempts have been made to increase the isotactic polymer content of the polymerisate resulting from polymerization or copolymerization of these alpha-olefins, and reduce the atactic polymer content.
One suggested way of doing this is to improve the stereospecificity of the Zigeler-Natta catalyst consisting of a titanium chloride, such as titanium trichloride, and an organic aluminium compound, such as alkyl aluminium or alkyl aluminium chloride, by adding stereospecificity additives to it; this modified catalyst encourages production of a polymerisate made up almost entirely of isotactic polymer.
The many such additives recommended to improve stereospecificity of catalysts consisting of a titanium chloride and an organic aluminium compound include phosphines, such as triphenylphosphine and tributylphosphine, amines, more specifically tertiary-amines such as triethylamine, tributylamine and N,N-dimethylaniline, ethers for example dialkylethers such as diethylether, dipropylether, or alkylene oxides such as tetrahydrofurane, and thioethers, for example dialkylthioethers and diarylthioethers such as diethylthioether or dipropylthioether, or alkylene thioethers such as tetrahydrothiophene.
But although these stereospecificity additives are effective in the sense that they improve the stereospecificity of the Ziegler-Natta catalyst and provide high-isotacticity polyolefins, in a number of cases they cause a serious reduction in catalyst activity, in other words a drop in the quantity of polymer produced for a given quantity of catalyst. This is a major drawback, seriously affecting the profitability of the polymerization process.
This invention offers a polymerization process of the type described in which particular stereospecificity additives are used to produce polymers or copolymers of alpha-olefins containing 3 to 8 carbon atoms with high isotacticity index, while keeping the catalyst sufficiently active, and in which, in a specially recommended embodiment of the invention, these additives are combined with a compound acting as activator, producing very high yields of high-isotacticity polymer.
This new process to make polymers or copolymers of alpha-olefins containing from 3 to 8 carbon atoms with a high isotacticity index, by polymerization of an alpha-olefin containing 3 to 8 carbon atoms, sequence copolymerization of such alpha-olefins with one another and/or with ethylene, or copolymerization of mixtures of such alpha-olefins with one another and/or with ethylene, such mixtures containing at least 85 moles percent of one such alpha-olefin, using a catalyst consisting of a titanium chloride combined with an organic aluminium compound, in the presence of a stereospecificity additive, is characterized by the fact that this stereospecificity additive is a compound with the general formula: EQU R.sub.1 --O--(C.sub.p H.sub.2p)--S--R.sub.2
where:
p is an integer from 1 to 6, PA0 R.sub.1 et R.sub.2 are identical or different alkyl radicals containing 1 to B 4 carbon atoms, or are linked together to form a divalent --(C.sub.m H.sub.2m)--radical, PA0 where: m is an integer from 1 to 6. PA0 Y is an alkyl radical containing 1 to 8 carbon atoms, a cycloalkyl radical containing 4 to 8 carbon atoms, or an aryl radical containing 6 to 8 carbon atoms, PA0 X is a halogen atom, such as a chlorine atom, and a is a number equal to 1, 1.5, 2 or 3. PA0 reduction of titanium tetrachloride by a metal such as aluminium or titanium, the reduced product possibly being ground; PA0 reduction of titanium tetrachloride by hydrogen; PA0 reduction of titanium tetrachloride by an organo-metallic compound such as alkyl aluminium; PA0 ethylthiomethoxyethane (C.sub.2 H.sub.5 --S--CH.sub.2 --CH.sub.2 --O--CH.sub.3), PA0 n is an integer, the same as or different from m, and equal in value from 1 to 6, PA0 m and n preferably each being equal in value from 1 to 4. PA0 dry grinding together of the additive with titanium trichloride in violet form (obtained by reducing titanium tetrachloride with a metal, such as aluminium) in a ball-mill; PA0 mixing the additive while being agitated with a titanium trichloride in violet form in an inert diluent, such as a saturated hydrocarbon like heptane, hexane or mineral oil; PA0 mixing the additive while being agitated with a titanium chloride in beta form (obtained by reducing titanium tetrachloride with an alkyl aluminium) in an inert diluent, such as a saturated hydrocarbon, then, after the diluent has evaporated, collecting the beta titanium trichloride containing the additive using titanium tetrachloride, at 70.degree. to 130.degree. C., to obtain a violet titanium trichloride containing the additive; PA0 mixing the additive while being agitated with a titanium trichloride in violet form in an inert diluent, such as a saturated hydrocarbon like hexene or heptane, at a temperature of approximately 40.degree. C., then collecting it using titanium tetrachloride in an inert diluent at approximately 65.degree. C.; PA0 forming a composition by mixing the additive and titanium tetrachloride in given proportions, then grinding this composition together with anhydrous magnesium chloride (as substrate), and finally treating the resulting crushed powder with an alkyl aluminium which may or may not contain a stereospecificity additive, to produce a supported titanium trichloride containing the additive.
Alpha-olefins containing 3 to 8 carbon atoms suitable for such polymerization or copolymerization have the formula: CH.sub.2 .dbd.CH--R,
where: R is an alkyl radical containing 1 to 6 carbon atoms.
Such alpha-olefins comprise propylene, 1-butene, 1-pentene, 4-methyl 1-pentene, and 1-hexene. By means of this new process, high-isotacticity homopolymers may be obtained by polymerizing a single alpha-olefin, or high-isotacticity sequence copolymers by various sequence copolymerization processes to copolymerize one such alpha-olefin with ethylene or at least two such alpha-olefins with or without ethylene, or, finally, high-isotacticity random copolymers by copolymerizing a mixture of one such alpha-olefin with ethylene or a mixture of at least two such alpha-olefins with or without ethylene, provided that the proportion of alpha-olefins containing 3 to 8 carbon atoms or of one such alpha-olefin containing 3 to 8 carbon atoms in the mixture is at least 85 moles percent. High-isotacticity polymers or copolymers obtained by this new process comprise polypropylene, 1-polybutene, 1-polypentene, poly(4-methyl 1-pentene), random copolymers of propylene and ethylene, propylene and 1-butene, propylene and 4-methyl 1-pentene, or propylene and 1-hexene, containing more than 85 moles percent propylene, and sequence copolymers of propylene and ethylene, propylene and 1-butene, or 1-butene and ethylene.
The organic aluminium compound forming one ingredient of the catalyst for this process is preferably a compound with the general formula: EQU Al Ya .times.(3-a),
where:
Recommended compounds of this type are those with the formulae: Al Y.sub.2 Cl and Al Y.sub.3, where: Y has the meaning already defined, more specifically a phenyl or cyclohexyl radical, or an alkyl radical containing 2 to 6 carbon atoms, such as ethyl, propyl, isopropyl, butyl, isobutyl and hexyl. Such compounds comprise in particular diethylaluminium chloride, dibutyl aluminium chloride, triethyl aluminium, tripropyl aluminium, tributyl aluminium, and tri-isobutyl aluminium.
The titanium chloride combined with the organic aluminium chloride is preferably a titanium trichloride, which may be any titanium trichloride known in the existing art as a component of Ziegler-Natta catalysts. This titanium trichloride may be obtained by the following methods in particular:
grinding a mixture of titanium trichloride and a halide of a metal in column III of the Periodic Table of Elements, such as an aluminium halide.
Titanium trichloride is modified by being treated in the presence of compounds such as tertiary amines, camphor, dialkyl ethers, or phosphorus compounds such as phosphorus oxychloride, are also suitable for use in this new process.
Stereospecificity additives suitable for this new process, and defined by the general formula given above, comprise linear compounds such as:
methylthiomethoxyethane (CH.sub.3 --S--CH.sub.2 --CH.sub.2 --O--CH.sub.3), PA1 propylthiomethoxyethane (C.sub.3 H.sub.7 --S--CH.sub.2 --CH.sub.2 --O--CH.sub.3), PA1 ethylthioethoxyethane (C.sub.2 H.sub.5 --S--CH.sub.2 --CH.sub.2 O--C.sub.2 H.sub.5),
or cyclic compounds with the formula: ##STR1## where: m has the meaning already defined, and
Such compounds includes: ##STR2##
The catalyst may be used without any substrate, or may be deposited on or fixed to an inorganic or organic substrate, for example fixed to an inorganic substrate, such as a metal oxide, carbonate or hydroxychloride like magnesium oxide, magnesium carbonate or magnesium hydroxychloride.
The quantity of stereospecificity additive required is such that the ratio of the number of titanium atoms to the number of additive molecules in the polymerization mixture is between 0.01 and 100, and preferably between 1 and 70.
The proportions of titanium trichloride and organic aluminium compound may vary widely depending on whether or not the catalyst is on a substrate. For example, when a catalyst with substrate is used, the ratio of the number of aluminium atoms to the number of titanium atoms in the polymerization mixture is between 1 and 500, and preferably between 50 and 200. When a catalyst without substrate is used, this ratio is between 1 and 10, and preferably between 2 and 5.
The catalyst may be preformed before being added to the polymerization mixture. but in some cases it may be formed in situ in the polymerization mixture. Whether preformed before addition to the mixture or formed in situ, the whole preformed catalyst or all its components may be added to the polymerization mixture at the beginning of polymerization, or in fractions or continuously throughout polymerization.
There are no special requirements concerning incorporation of the stereospecificity additive in the polymerization mixture, and various methods may be used. For example, when a catalyst consisting of a titanium chloride, such as titanium trichloride, and organic aluminium compound is preformed before injection into the polymerization mixture, the stereospecificity additive may be added to the titanium chloride and organic aluminium compound, by mixing all three components directly or by premixing the additive with one of the other two components and subsequently adding the remaining component, and the resulting mixture injected into the polymerization mixture, or else the stereospecificity additive may be injected into the polymerization mixture first, followed by the titanium chloride and organic aluminium compound mixture.
When the titanium chloride and organic aluminium compound are injected separately into the polymerization mixture to form the catalyst in situ, the stereospecificity additive may either be added separately to the polymerization mixture, or mixed with the titanium chloride or organic aluminium compound before they are injected into the polymerization mixture.
When the additive is premixed with the organic aluminium compound, this is done by placing the additive and compound in solution in an inert solvent, such as a hydrocarbon like heptane. The resulting solution can then easily be injected into the polymerization mixture.
When the additive is to be premixed or made into a composition with the titanium chloride, such as a titanium trichloride, before being added to the polymerization mixture, this is preferably done by techniques such as those summarized below:
Compositions containing a titanium chloride, such as titanium trichloride or titanium tetrachloride, and an additive suitable for use in this new process, such as those obtained by the methods described above, may be prepared just before use, or prepared in advance and stored in the form of suspension in an inert diluent, such as a saturated hydrocarbon like hexane, heptane or mineral oil. These compositions are injected into the polymerization medium in the form of a suspension in an inert diluent such as a saturated hydrocarbon like hexane, heptane or mineral oil.
In one recommended embodiment of the invention, providing higher yields than in the presence of the additive alone, and without reducing the isotacticity index of the polymerization, the polymerization medium may contain one more activators selected from the group comprising acyclic or cyclic polyenes and dihydrocarbylacetylenes in which the hydrocarbyl radicals are selected from aryl radicals containing 6 to 16 and preferably 6 to 8 carbon atoms, and alkyl radicals containing 1 to 16 and preferably 1 to 8 carbon atoms. Compounds functioning as activator, in other words increasing the quantity of polymer produced for a given quantity of catalyst consisting of titanium chloride and organic aluminium compound catalyst, comprise more specifically cyclo-octadiene, 1,3,5-cycloheptatriene, cyclododecatriene, cyclo-octatetraene, 3-methyl 1,4,6-heptatriene, diphenylacetylene, ditolylacetylene, methylphenylacetylene, dimethylacetylene, diethylacetylene, dipropylacetylene, dibutylacetylene, dihexylacetylene and dioctylacetylene.
The proportion of activator in the polymerization mixture can vary quite considerably, but is preferably such that the ratio of the number of titanium atoms to the number of molecules of activator in the polymerization mixture is between 0.01 and 100, and preferably between 1 and 70.
The activator may be added to the polymerization mixture in the same way as the stereospecificity additive, either separately from or mixed with the additive.
Consequently, additive and activator may be injected into the polymerization mixture separately from each other and separately from the catalyst components. Alternatively, the additive may be injected after being mixed with one of the catalyst components, while the activator is injected with the other component, or alone, or the activator is injected after being mixed with one catalyst component, while the additive is injected alone. Additive and activator may also be injected together after being mixed with either catalyst component. For example, additive and activator may be injected together after being mixed with the titanium chloride. In this case the composition or premixture of titanium chloride, additive and activator is preferably prepared by methods similar to those summarized above for premixing of titanium chloride and additive.
In such compositions containing titanium chloride, additive and activator, which may be prepared just before use or made in advance, stored and used in suspension in an inert diluent such as a saturated hydrocarbon like heptane, hexane or mineral oil, as well as in the corresponding preformed compositions already mentioned and not containing any activator, the proportions of titanium compound, additive and possibly activator are preferably such that the respective ratios of the number of titanium atoms to the number of molecules of additive and to the number of molecules of activator are between 0.01 and 100, and preferably between 1 and 70.
In addition, in compositions containing titanium chloride, additives and activator, the relative proportions of additives and activator are preferably such that the ratio of the number of additive molecules to the number of activator molecules is between 0.2 and 5, and preferably between 0.5 and 2.
The relative proportions of additive and activator in the polymerization mixture may also vary quite considerably, but are preferably such that the ratio of the number of additive molecules to the number of activator molecules is between 0.2 and 5, and more specifically between 0.5 and 2.
Polymerization, in other words the process by which the alpha-olefin or alpha-olefins are brought into contact with the catalyst in the presence of the additive and possibly activator to produce polymer or copolymers, may be performed under normal conditions as known in the existing art.
For example, the polymerization temperature may be between 0.degree. and 150.degree. C., and preferably between 40.degree. and 120.degree. C., with absolute pressure ranging from slightly above atmospheric pressure to approximately 100 bars.
Polymerization may be performed either in an inert liquid phase such as an inert hydrocarbon like hexane, heptane or benzene, or using the alpha-olefin or mixture of alpha-olefins to be polymerized, kept in a liquid state, as polymerization mixture, or using a gas phase. When polymerization is done in an inert liquid phase, polymerization pressure is usually less than approximately 15 to 20 bars; on the other hand, when the alpha-olefin or mixture of alpha-olefins to be polymerized is used as polymerization mixture, much higher pressures are applied, so as to keep the alpha-olefin or mixture of alpha-olefins in a liquid phase. For example, when a liquid propylene phase is used, polymerization pressure is usually about 30 bars.
The molecular weights of polymers can be adjusted by using standard transfer agents, such as hydrogen.
When polymerization is completed, the polymerisate is deactivated and separated from the polymerization mixture, and if necessary undergoes additional purification treatment, using any existing techniques. The method described in French patent application No. 76 21 292 (Publication No. 2 358 423) of July 12, 1976, in the applicant's name, may be used for separation and purification of the polymer produced by a propylene polymerization process.
Alpha-olefin polymers and copolymers obtained by means of this new process are characterized by high isotacticity index and high yields.
The isotacticity index of a polymer means the percentage ratio of the weight of solid residue left after extraction of the polymer in n-heptane in a Soxhlet apparatus for 2 hours to the weight of polymer before undergoing this extraction process. The isotacticity index corresponds to the percentage weight of the isotactic fraction of the polymer.